Acrylonitrile-butadiene-styrene (hereinafter, referred to as ABS) resins are widely used as exterior materials of electric and electronic products and office machines and the like due to rigidity and chemical resistance of acrylonitrile, and processability and mechanical properties of butadiene and styrene. However, the ABS resin is inherently readily combustible and has almost no flame retardancy. Due to these problems, the ABS resin used for electric and electronic products, office equipment and the like should satisfy flame-retardancy standards in order to secure fire safety of electric and electronic products.
In regard to such flame-retardancy standards and flame retardancy test methods, there is a vertical combustion test method according to UL 94 to evaluate flame resistance against internal ignition due to electrical short, short circuit, and the like of a circuit substrate inside finished electronics.
As methods for imparting flame retardancy to ABS resins, there are a method of polymerizing a rubber-modified styrene resin through incorporation of a flame-retardant monomer during preparation of a rubber-modified styrene resin, a method of mixing a flame retardant and an auxiliary flame retardant with the prepared rubber-modified styrene resins, and the like. Examples of the flame retardant include halogen-based flame retardants such as bromine-based and chlorine flame retardants, and non-halogen flame retardants such as phosphorous, nitrogen and hydroxide flame retardants. Examples of the auxiliary flame retardant include antimony compounds, silicon compounds, zinc compounds and the like.
Thereamong, halogen flame retardants exhibit high flame retardancy, as compared to non-halogen flame retardants, and may maintain mechanical properties of rubber-modified styrene resins. At present, a method of imparting flame retardancy to ABS resins using halogen flame retardants is the most generally used. Thereamong, bromine-based flame retardants are particularly effective. However, when a bromine-based flame retardant is added during processing of ABS resins, thermal stability is deteriorated and the flame retardant is decomposed due to high temperatures and pressures during processing, thus causing generation of toxic corrosive gases and negatively affecting work environments and human health. This problem also occurs when the ABS resin processed by incorporating a bromine-based flame retardant combusts.
In an attempt to avoid this problem, a non-halogen flame retardant is used and, in particular, a phosphorous-based flame retardant is generally used. However, when a phosphorous-based flame retardant is used, flame retardancy thereof is low, compared to halogen flame retardants, and thus, a large amount of phosphorous-based flame retardant should be used. In addition, thermoplastic resin compositions which do not produce char due to the principle of phosphorous-based flame retardant systems cannot sufficiently exert flame retardancy. In addition, generally used phosphate compounds, such as triphenyl phosphate, tricresyl phosphate, tri(2,6-diphenyl phosphate), tri(2,4,6-trimethylphenyl)phosphate, etc., as a phosphorous-based flame retardant have plasticization effects to resins, and thus, overall heat deflection temperature (HDT) of a resin is decreased.
In addition, when a phosphorous-based flame retardant and an epoxy-based resin as a char generation material are added to a thermoplastic resin composed of an ABS copolymer and a SAN copolymer, flame retardancy is enhanced, but heat deflection temperature and rigidity are low, compared to flame-retardant ABS products to which generally used halogen-based retardants are applied.